Thermoforming aids

ABSTRACT

A thermoforming aid for use in creating a thermoformed impression of an object such as a dental arch. The thermoforming aid has a thermoformable sheet which has inherent tendency to curl, and a curl-resistant element which prevents the thermoformable sheet from curling. The thermoforming aid makes a person&#39;s task of placing a sheet of thermoformable material, especially a very thin sheet having an inherent tendency to curl, in proper position in a thermoforming machine less difficult and less time-consuming.

DOMESTIC PRIORITY CLAIM

This application claims priority of pending patent application Ser. No.14/703,475, filed May 4, 2015, and the entirety of that patentapplication is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to thermoforming, and in particular tothermoforming aids which keep sheets of thermoformable material fromcurling when placed in thermoforming machines.

BACKGROUND OF THE INVENTION

Thermoforming is a process for creating various products by heatingthermoformable material and causing the heated material to form onto atleast a portion of an object and create an impression of at least aportion of the object in the thermoformable material. The thermoformablematerial may be a sheet which is placed in a thermoforming machine whichwhen operated, heats the thermoformable sheet and causes the heatedthermoformable sheet to form onto at least a portion of the object andcreate an impression of at least a portion of the object in the heatedthermoformable sheet. A vacuum may be used to draw the heated sheet intointimate contact with the object. The impression created in the sheet isretained when the sheet cools.

Thermoforming machines are commonly used in dentists' offices and dentallaboratories for creating thermoformed impressions of objects used inthe practice of dentistry which includes not only general dentistry butalso dental specialties such as orthodontia for example. Applicant'sU.S. Pat. No. 9,526,591, issued Dec. 27, 2016, discloses a method ofthermoforming a thin sheet of thermoformable material onto a dental archmodel.

A typical practice for using a thermoforming machine involves manuallyplacing a perimeter margin of a thin sheet of thermoformable material onan open-center platen of the machine and closing an open-center coveronto the perimeter margin of the sheet to hold the sheet in properposition for thermoforming onto an object such as a dental arch model.The thermoforming machine comprises a base on which the object isplaced. With a sheet of thermoformable material held between the platenand the cover, the sheet is heated and begins to droop. With the platenand the closed cover holding the perimeter margin of the sheet, they aremoved downward to drape the drooping sheet over the object whilecooperating with the base to form a closed space within which the objectis disposed with the sheet draped over it. Vacuum is then drawn withinthe closed space through multiple passages in the base to cause thedraped sheet to more intimately form onto the object. After that, thevacuum is turned off and the sheet is allowed to cool. Upon completionof cooling, the formed sheet is removed from the object, retaining animpression of the object.

When the object is a model of a dental arch, or portion of such a model,an impression of teeth of the model, and any devices which may beaffixed to the model, are captured in fixed form in the thermoformedmaterial. As described in the above-mentioned patent, devices such asorthodontic brackets which are releasably mounted on the model may becaptured in the thermoformed material and separate from the model alongwith the thermoformed material during removal of the material from themodel.

Thinness of a sheet of thermoformable material may be an importantfactor in the quality of a resulting impression because it can affectthe ability of the thermoformable material to form around an object witha desired degree of precision. In general, a very thin sheet can beformed around an object with greater precision than can a thicker sheet.

SUMMARY OF THE DISCLOSURE OF THE INVENTION

A very thin sheet of certain thermoformable materials has an inherenttendency to curl. That tendency can make proper placement of the sheeton the platen of a thermoforming machine by a person difficult and timeconsuming.

Briefly, this disclosure introduces novel thermoforming aids for use inthermoforming machines to create impressions of at least portions ofobjects, a dental arch model being one example of such an object.

These aids make a person's task of placing a sheet of thermoformablematerial, especially a very thin sheet having an inherent tendency tocurl, in proper position in a thermoforming machine less difficult andtime-consuming.

The foregoing summary is accompanied by further detail of the disclosurepresented in the Detailed Description below with reference to thefollowing drawings which are part of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a first example of a thermoforming aid foruse in a thermoforming machine.

FIG. 2 is front elevation view of the thermoforming aid of FIG. 1.

FIG. 3 is front elevation view as in FIG. 2, but showing a beginning ofan initial step of removing a first element of the thermoforming aid forenabling the thermoforming aid to be placed in a thermoforming machine.

FIG. 4 is front elevation view as in FIG. 3, but with the first elementremoved.

FIG. 5 is a top plan view of a platen of a thermoforming machine.

FIG. 6 is a cross section view in the direction of arrows 6-6 in FIG. 5.

FIG. 7 is a top plan view showing the thermoforming aid of FIG. 4 havingbeen placed on the platen of FIG. 5.

FIG. 8 is a view in the direction of arrows 8-8 in FIG. 7 showing abeginning of a step of removing a second element from the thermoformingaid.

FIG. 9 is view as in FIG. 8 but showing the second element removed.

FIG. 10 is a top plan view of a full dental arch model.

FIG. 11 is a perspective view of a thermoforming machine showing thedental arch model placed on a base of the machine.

FIGS. 12-14 show a sequence of steps performed by the thermoformingmachine during a thermoforming operation.

FIG. 15 is a top plan view of a second example of a thermoforming aidfor use in a thermoforming machine.

FIG. 16 is a cross section view in the direction of arrows 16-16 in FIG.15.

FIG. 17 is a view showing the example of FIG. 16 in place on athermoforming machine.

DETAILED DESCRIPTION

FIG. 1 and FIG. 2 show a first example of a thermoforming aid 20 for usein a thermoforming machine. The rectangular shape shown in FIG. 1 isrepresentative of one particular shape for use in a machine having arectangular platen, but other shapes, such as circular or oval, would beappropriate for platens of other shapes. For clarity of illustration,the thickness shown in FIG. 2 is greatly exaggerated when compared withthe length and width shown in FIG. 1.

Thermoforming aid 20 comprises a rectangular thermoformable sheet 22, acurl-resistant element 24, and a release cover 26. Thermoformable sheet22 has an upper surface 28 and a lower surface 30. Curl-resistantelement 24 has an upper surface 32 and a lower surface 34. Release cover26 has an upper surface 36 and a lower surface 38. Lower surface 34 ofcurl-resistant element 24 is disposed in full surface-to-surface contactwith upper surface 28 of thermoformable sheet 22. Lower surface 30 ofthermoformable sheet 22 is disposed in surface-to-surface contact withupper surface 36 of release cover 26.

Thermoformable sheet 22 has a thickness, as measured between its uppersurface 28 and its lower surface 30, selected to obtain a desiredcharacteristic, such as degree of precision, in a finished impression ofan object onto which it is ultimately formed. Certain thermoformablematerials in sufficiently thin sheet form possess an inherent tendencyto curl when unsupported. Curling has different degrees ranging frompartial curling of a perimeter edge of a sheet which doesn't form a fullconvolution, to curling of a perimeter margin into one or moreconvolutions of a roll.

Curl-resistant element 24 possesses resistance to curling which, throughits surface-to-surface contact with thermoformable sheet 22, preventsthermoformable sheet 22 from curling as it otherwise would duringplacement by itself on a platen of a thermoforming machine without acurl-resistant element to keep it from curling. The description ofelement 24 being curl-resistant should not be construed to imply that itmust necessarily be flat and rigid and keep the thermoformable sheetflat. Indeed, element 24 may be a thin sheet of material which, as awhole, can flex or warp to a limited extent without its perimeter margincurling.

In preparation for using thermoforming aid 20, release cover 26 isremoved. Release cover 26 has a perimeter margin, at least a portion ofwhich extends beyond the perimeter margin of thermoformable sheet 22. Inthe disclosed embodiment, the complete perimeter margin of release cover26 extends beyond the perimeter margin of thermoformable sheet 22 toenable a portion of the perimeter margin of release cover 26 to bepartially separated from sheet 22 as suggested by FIG. 3 and thengripped between a person's thumb and forefinger and peeled completelyoff sheet 22, leaving thermoforming aid 20 as shown in FIG. 4.

Removal of release cover 26 exposes a material on lower surface 30 ofthermoformable sheet 22 which gives it some degree of tenacity, as willbe further explained hereinafter. The exposed material extendscompletely around the perimeter margin of sheet 22, leaving a centerzone free of the exposed material.

FIG. 5 shows a top plan view of a platen 40 of a thermoforming machine42, an example of which is shown in FIG. 11. Platen 40 has a rectangularshape which surrounds an open rectangular center 44 as also seen in FIG.6.

FIG. 7 shows thermoforming aid 20 placed on platen 40 after releasecover 26 has been removed. The material on surface 30 of sheet 22 whichis exposed by removal of release cover 26 may be an adhesive whichendows sheet 22 with sufficient tenacity to be held fast in the flatposition in which it is placed on the flat top surface of platen 40while allowing it to be pulled off the platen after thermoforming.

Curl-resistant element 24 completely covers thermoformable sheet 22 toplace the latter's entire upper surface 28 in surface-to-surface contactwith the former's lower surface 34. Element 24 has a perimeter margin atleast a portion of which extends beyond the perimeter margin of sheet22, and which in the disclosed embodiment comprises a tab 46 at onecorner.

As suggested by FIG. 8, tab 46 provides a gripping portion of element 24which can be gripped between a person's thumb and forefinger and pulledupward to peel element 24 off thermoformable sheet 22 while the tenacityof the sheet to platen 40 is sufficient to keep the sheet in place onplaten 40 as shown in FIG. 9. A certain degree of care in peelingelement 24 off sheet 22 may be appropriate depending on materials,thicknesses, and tenacity of the margin of thermoforming aid 20 to theplaten because the adherence of sheet 22 to the platen is intended to beonly temporary, not permanent, so as to allow the margin to beconveniently removed from the platen after thermoforming has beencompleted. If one hand is peeling element 24 too rapidly or tooforcefully without digits of the other hand aiding to hold down aportion which has yet to be peeled off, a portion of sheet 22 may beinadvertently pulled off the platen. Consequently, because the adherenceof sheet 22 to the platen is intended only to temporarily constrain thesheet against sliding on and separating from the platen until element 24has been completely peeled off, it is generally preferred that element24 be slowly peeled off sheet 22 using thumb and finger of one handwhile one or more digits of the other hand are pressing down on portionsof the perimeter margin of element 24 which have yet to be peeled off.

A dental arch model 48, shown by itself in FIG. 10, is also shown inFIG. 11 placed on a base 50 of thermoforming machine 42.

FIGS. 12-14 illustrate further steps in a thermoforming process forcreating an impression of dental arch model 48 in sheet 22.

With the perimeter margin of sheet 22 disposed on platen 40 as has beenexplained, a cover 52 is closed onto the perimeter margin of the sheetas in FIG. 11. Both platen 40 and cover 52 can move up and down on anupright post 54. At the top of post 54 is a heater 56 which can turnhorizontally on post 54. Heater 56 is swung from the position shown inFIG. 11 to overlie sheet 22 and with sheet 22 held between platen 40 andcover 52, they are moved from the position shown in FIG. 11 to the oneshown in FIG. 12. Heater 56 is operated to begin heating the sheet andsoftening it while its perimeter margin continues to be held between theplaten and cover. After sufficient softening of the sheet, the platenand cover are moved downward to drape the drooping sheet 22 over model48 as in FIG. 13.

When platen 40 is brought into contact with base 50, a closed spacecontaining model 48 with sheet 22 draped over it is created by base 50,platen 40, and the softened sheet 22. A pump 58 is then operated, as inFIG. 14, to draw vacuum within the closed space through multiplepassages 60 in base 50, causing the draped sheet 22 to intimately formonto model 48. The size of sheet 22 is large enough to cover the cusps,lingual, and labial surface of the teeth and the gum line in thisparticular example. After that, pump 58 is turned off and sheet 22 isallowed to cool. Upon completion of cooling, the formed sheet is removedfrom the model, retaining an impression of the model.

The impression may in some instances be further processed and/or put tofurther uses as described in the above-mentioned patent.

FIG. 15 and FIG. 16 show a second example of a thermoforming aid for usein a thermoforming machine. This example comprises a thermoformablesheet 22 and a curl-resistant element 62 having an open center 64. Anupper surface of element 62 has full surface-to-surface contact with theentire perimeter margin of the lower surface of sheet 22. Element 62 hasa flat lower surface which is treated with an adhesive which whenexposed by removal of a release cover 66, provides some degree ofadherence when placed on the platen. Hence, this second example differsfrom the first in that the curl-resistant element remains in place whenthe thermoforming machine is operated. FIG. 17 shows this example inplace on a platen 40 of a thermoforming machine.

Examples of thermoformable materials which, in sufficiently thin sheetform, have an inherent tendency to curl include starches, gelatins, andpolyvinyl alcohol. Those materials are dissolvable in water and can bedissolved when placed in a person's mouth as described in theabove-mentioned patent. One specific example of thermoforming aid 20comprises a starch sheet 22 having a thickness of approximately 0.004inch and a polyester sheet of approximately 0.010 inch thickness ascurl-resistant element 24.

The property of an embodiment to adhere to a platen can be provided byother than an adhesive applied to sheet 22 as in the first example or tocurl-resistant element 62 as in the second example. Certainthermoformable materials and curl-resistant materials can adhere to aplaten by static electricity which is imparted during a laminationprocess which is used in the manufacture of thermoforming aid 20 and/orsurface friction of either the material which is placed on the platenand/or the platen itself. Certain platens have a groove in their uppersurfaces surrounding their open centers. A rubber-based gasket, orequivalent, is disposed in the groove with the upper surface of thegasket substantially flush with the upper surface of the platen. Thematerial of thermoforming aid 20 which is placed on such a gasket has acharacteristic which when placed on the gasket possesses its own surfacefriction which allows surface friction of the gasket to hold thethermoformable sheet in place.

The two examples may be manufactured by a lamination process in whichthe sheet and the curl-resistant element are laminated by rollers.Pressure of the rollers applied to the materials being laminated can besufficient to cause the laminates to remain in releasablesurface-to-surface contact without use of adhesive. Alternately they canbe laminated together using a release adhesive.

What is claimed is:
 1. An article for use in creating a thermoformedimpression of an object, the article comprising: a thermoformable sheethaving a thickness which, as measured between an upper surface and alower surface, creates an inherent tendency for the thermoformable sheetto curl, a curl-resistant element which has an upper surface and a lowersurface, one of which is disposed in surface-to-surface contact with oneof the surfaces of the thermoformable sheet, and which through thesurface-to-surface contact with the thermoformable sheet, prevents thethermoformable sheet from curling, and the lower surface of one of thethermoformable sheet and the curl-resistant element comprising aperimeter margin having a property of adhering to an underlying surfacewhen placed against such an underlying surface.
 2. An article as setforth in claim 1 in which the lower surface of the curl-resistantelement is disposed in surface-to-surface contact with the upper surfaceof the thermoforrriable sheet, and the perimeter margin of the lowersurface of the thermoformable sheet has a property for adhering to anunderlying surface when placed on such an underlying surface.
 3. Anarticle as set forth in claim 2 in which the property for adhering to anunderlying surface is provided by adhesive disposed on the perimetermargin of the lower surface of the thermoformable sheet, thethermoforming aid further comprising a release cover releasably coveringthe adhesive.
 4. An article as set forth in claim 3 in which the releasecover has a perimeter margin, at least a portion of which extends beyondthe perimeter margin of the thermoformable sheet.
 5. An article as setforth in claim 4 in which the adhesive is disposed along the perimetermargin of the lower surface of the thermoformable sheet, and the lowersurface of the thermoformable sheet has an adhesive-free center zonewhich is bounded by the adhesive.
 6. An article as set forth in claim 2in which the curl-resistant element has a perimeter margin at least aportion of which extends beyond the perimeter margin of thethermoformable sheet.
 7. An article as set forth in claim 6 in which thecurl-resistant element has surface-to-surface contact with the entireupper surface of the thermoformable sheet.
 8. An article as set forth inclaim 7 in which the curl-resistant element comprises a tab extendingbeyond the curl-resistant sheet's surface-to-surface contact with theentire upper surface of the thermoformable sheet.
 9. An article as setforth in claim 1 in which the perimeter margin of the curl-resistantelement surrounds an open-center zone, the upper surface of thecurl-resistant element is disposed in surface-to-surface contact withthe lower surface of the perimeter margin of the thermoformable sheet,and the lower surface of the perimeter margin of the curl-resistantelement has a property of adhering to an underlying surface when placedon such an underlying surface.
 10. An article as set forth in claim 9 inwhich the property for adhering to an underlying surface is provided byadhesive disposed on the perimeter margin of the lower surface of thecurl-resistant element, and further comprising a release coverreleasably covering the adhesive.
 11. An article as set forth in claim 1in which material of the thermoformable sheet comprises one of starch,gelatin, and polyvinyl alcohol.
 12. An article as set forth in claim 1in which the curl-resistant element comprises a polyester sheet.
 13. Anarticle as set forth in claim 1 in which material of the thermoformablesheet possesses releaseable adherence to an underlying surface.